Film reader

ABSTRACT

This invention presents a film reader equipped with a reflecting type screen, which is arranged in a housing of the reader and has a number of ring strip surfaces having different inclination angles and arranged concentrically. The common center of the ring strip surfaces is deviated from the center of the screen and locates outside of the screen and the end of the screen nearest to the common center is placed near to an observing aperture in the housing. A light source for illuminating a microfilm having recorded images and an optical system for projecting the image of the illuminated film to the screen are provided. Further, the screen is formed by one synthetic resin or preferably at least two kinds of synthetic resins having different refractive indices and mutually non-soluble property. A reflecting substance may be mixed with said resins.

This is a continuation of application Ser. No. 884,536, filed Mar. 8,1978 now U.S. Pat. No. 4,229,085.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a film reader equipped with a reflecting typescreen.

2. Description of the Prior Art

Film readers, which enable to observe an enlarged image projected on ascreen of the image recorded on a microfilm, are classified into twokinds according to the type of the screen to be used. One kind of filmreaders uses the so-called transmitting type screen comprising atransparent glass plate or synthetic resin plate providing with aphotodiffusion layer on one surface thereof. This kind of readers iscalled as a transmitting type reader by which an image on a microfilm isprojected on one side of said transmitting type screen and a light imagetransmitting the screen is observed from the opposite side of thescreen. The other kind of readers is called as a reflecting type readerwhich uses the so-called reflecting type screen similar to a moviescreen. An image on a film is projected on said screen, and a lightimage reflected by the screen is observed from the same side of theprojecting surface. The reflecting type reader is more attractive thanthe transmitting type reader as it is easier to see a projected imagethan in the latter type. In the former type film reader, an observer isable to see a projected image keeping the state reading a printed mattersuch as a book, etc. However, the reflecting type film reader does notgive always the most suitable projected image, because it is inevitableto deteriorate the contrast of a projected image by a peripheralexternal light other than an image projecting light incident on thescreen, and further there has been no satisfactory device to reduce theinfluence of such external light. In the conventional reflecting typefilm reader, a large aperture for observation is provided at a portionof a square housing and a screen provided within the housing is observedthrough said aperture, so that when the reader is used in a light place,a light external of the reader comes into the housing through theaperture and impinges on the screen, and this incident light goes towardthe eyes of the observer, who will then observe both of the image lightand this peripheral light. As a result, the contrast of the imagebecomes significantly degraded and the brightness of the image becomesnon-uniform because the lightnesses before the screen and inside of thescreen on which the peripheral light impinges are different from eachother.

According to the conventional reflecting type film readers, there havebeen proposed the combination of a screen having a high lightdiffuse-reflection characteristic with an external light control filter;or a high brightness screen having a specific uneven surface of a dottedor line form to reflect a part of the light to a certain direction orthe light brightness screen having a curved screen surface so as to keepthe intensity of the light reflected by the screen high relative to theexternal light. However, the screen combined with a filter has a limitin its effect because the intensity of an image projection light islimited, and an obtained image is degraded due to a ghost produced by alight reflected by the filter surface. And the high brightness screenproduces partially bright points so that a strong glittering phenomenonoccurs, which causes to deteriorate the image quality and fatigue of theobserver's eyes. These disadvantages are counted as defects in theconventional reflecting type microfilm readers although they are easy toobserve.

SUMMARY OF THE INVENTION

An object of the invention is to overcome said defects and to provide afilm reader having an improved lightness and contrast of an image.

Another object of the invention is to provide a film reader whichenables an observer to see an image projected on a screen in acomfortable position and which gives a high quality image to be readeven in a light place.

Further object of the invention is to provide a film readersubstantially reducing the influence of a peripheral light incident onthe screen so as to give a projected image of a uniform brithtness.

Another object of the invention is to provide a film reader whichenables to observe an image projected on the screen in relatively widefield and which does not produce an image distortion which would resultin a problem in practical use.

Further object of the invention is to provide a film reader having arelatively large aperture in the housing for observing the screen, thesurface of which can be easily cleaned.

The invention will be explained in detail with respect to embodimentsshown in the drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a perspective view of a film reader embodying theinvention;

FIG. 2 shows a cross section of the reader shown in FIG. 1;

FIG. 3 shows a front view of the screen used in the reader of FIG. 1;

FIG. 4 shows a cross section of the screen;

FIGS. 5A and B are drawings illustrating methods of producing saidscreen, FIG. 6 is to explain the light orientation state of the screen;

FIGS. 7 and 8 show cross sections of other embodiments of the screen,respectively; and

FIG. 9 shows graphs illustrating light orientation characteristics ofthe screens.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2 show an embodiment of the microfilm reader of the presentinvention.

The film reader comprises a hollow lower housing 1 and a hollow upperhousing 3 supported on the lower housing 1 by a leg 2. Within the lowerhousing 1, an illuminating lamp 4 of, for example, a halogen lamp, aspherical mirror 5 effectively reflecting the light coming from the lamp4, an insulating glass 6, condenser lenses 7 and 8, and a mirror 9,which directs upwardly the light from the lamp 4, are arranged as shownand these elements constitute an optical system for illuminating amicrofilm.

The upper housing 3 is a rectangular housing comprising a bottom wall 11fixed to the leg 2, opposite side walls 12 integrally formed with thebottom wall 11, a rear wall 13 and a top wall 14 integrally formed withthe side walls 12 and the rear wall 13. And in a front side wall of thehousing 3 there is provided an observing aperture 15 largely opened tothe outside. A reflecting mirror 22 and a reflecting type screen 23 arearranged in the housing 3, and the housing 3 forms a hood covering thesurroundings of the screen 23. An observer located at a predetermineddistance from the housing 3 can observe the screen 23 through theaperture 15. A projecting lens 21 is mounted on the bottom wall 11 ofthe housing 3 for focusing an image of a microfilm on the screen 23through the reflecting mirror 22. On the top surface of the lowerhousing 1, a fiche carrier 26 is provided movably in before and behindand right and left, the carrier having two plane glass plates 19 and 20sandwiching therebetween a mirofiche F. By moving the carrier 26, aspecific image in a mirofiche can be placed at a position to beilluminated by the light from the lamp. An arm 24 is arranged at thelower portion of the bottom wall 11 for supporting a cylindrical lensbarrel 25 constituting a lens assembly 21. A spring 27 presses the arm24 downwardly so that the lower end surface of the lens barrel 25 ispress-contacting with the upper glass plate 19 of the carrier 26. Thusthe distance between the film and the lens is always constant and thefilm is maintained at the focussing position even when the carrier ismoved. A lever 29 is provided for adjusting the focussing.

An aperture 30 is provided in the bottom wall 11 in a positioncorresponding to the lens assembly 21. The light from the lens assembly21 passes through this aperture 30 to the reflecting mirror 22 and isprojected on the screen 23 and incident onto the eyes E of an observer.The distance between the centre of the screen 23 and the eyes E is lessthan twice as much as a usual distance of distinct vision, i.e. 25 cm.In FIG. 2, a shows a projection optical axis.

FIGS. 3 and 4 show the screen 23 used in the embodiment of FIGS. 1 and2. The surface of the screen 23 is formed as a Fresnel surface where anumber of inclined surfaces are arranged to condensing the lightreflected by the screen within a certain area and is formed as a lightdiffusion surface or formed by a light diffusion substance fordiffusion-reflecting the incident light in a suitable light-orientationstate. The Fresnel surface of the screen 23 corresponds to the Fresnelsurface of a Fresnel type concave lens and consists of a plurality ofring strips concentric with each other as the center 34 of the Fresneloptical axis as the common center. The inclinations of the ring stripsurfaces on the same circles relative to the center 34 of the opticalaxis are the same, the inclination of each ring strip is different insuch a manner that the ring strips departing from the center 34 havelarger inclination angles. Each ring strip of the Fresnel surface is setto have an inclined surface to make the pupil of the projecting lens andthe observing position E to have an approximate conjugate relation withrespect to the reflecting surface so as to direct the light coming fromthe projecting lens assembly 21 and reflected by the reflecting mirror22 to the observing position outside of the housing. Further, thesurface is formed as an elliptic Fresnel surface or a spherical Fresnelsurface so as to condense the main reflected light coming from each ofthe Fresnel inclined surfaces consisting the whole screen surface at aposition having a distance less than twice as much as the distance ofdistinct vision from the center of the screen. The Fresnel surface ofthe screen reflects the projected light effectively toward the observingposition so that the whole screen surface as viewed from the observingposition is brightened and is made as a high quality image surface. Onthe other hand, the light coming externally of the projecting lens isreflected to the direction outside of the observing position and theinfluence of the light incident from the observing side to the image issignificantly reduced so that a good image contrast is maintained.

The substance of the screen has a light diffusion-reflecting propertyfor obtaining a suitable reflecting light orientation characteristictaking the distance between two eyes of an observer and the field of themoving eyes into consideration.

In the above explained microfilm reader, the image projecting lightincident on the screen 23 from the projecting lens is reflected andorientated toward the observing position located outside of the housingfrom the observing aperture 15 of the housing 3, while the most of theexternal light incident on the screen surface 23 from outside of thehousing is reflected to the inside of the housing so that the most ofthe reflected light toward the observing position from the screen isoccupied by the image light component and the image on the screen ishardly effected by the external light. Consequently, even when thereflecting type mirofilm reader of the invention is used in the lightplace, it is possible to maintain the high quality and high contrastimage.

The contrast of the enlarged image projected on the screen is determinedfundamentally by the projection and focussing relation due to thequality of the projecting lens etc., and by the light component comingfrom outside of the projecting lens.

The contrast determined fundamentally by the projecting system is set toVo and the actual contrast containing the change component due to theexternal light is set to V. Then,

    Vo=(Imax-Imin)/(Imax+Imin)

    V=(Imax-Imin)/(Imax+Imin+2I.sub.D),

where Imax is the intensity of the light component in the observingdirection of the light area of the image, Imin is that of the dark areaof the image, and I_(D) is the intensity of the light component in theobserving direction of the light coming externally of the projectinglens.

It becomes clear from the above relations, the intensity of the externallight incident on the screen will significantly affect the imagecontrast. Assuming that Imin=0 and therefore Vo=1, which shows the bestquality image, and the screen is of a quality nearly to a perfectdiffusion surface, when the external light of I_(D) =5 Imax is incidenton the screen, a very bad contrast image of V=1/11≈0.09 is obtained.

In a screen of a Fresnel type reflecting surface having a goodreflecting directivity, the reflecting component of the light directingto the observing position from the observing aperture is small asexplained in the foregoing, the deterioration of the contrast due to theexternal light is reduced. In a Fresnel reflecting screen using a lightdiffusive substance of the light orientation property shown by the curveD of FIG. 9, described hereinafter, under the condition of angle 30°formed by the projecting light and the main light reflected by thatsurface, the rate of the light orientation component relative to thepeak is 0.135, then I_(DO) =5 Imax, where I_(DO) is the intensity of theexternal light incident on the screen, and I_(D) =0.135 I_(DO), so thatV=0.67, which is about 7.5 times the contrast obtained by the screenhaving the surface nearly to the complete diffusion surface explained inthe foregoing. In actual, the most of the external light is not a spotlight source, but, according to this invention, a high contrast and highquality image is obtained.

Further, by suitably selecting the positional condition among the bodyof the microfilm reader, the housing covering the screen and theobserving aperture, a high contrast and high quality projected image canbe observed by an observer located at a comfortable position. Byconsidering the height of a desk on which the reader is placed and theposition of an observer, firstly the inclination angle of the screenrelative to the horizontal plane is set between 20° and 40°, andsecondly, the optical axis of the projecting lens incident onto thescreen is set to cross perpendicularly the surface of the screen, andthe angle formed between the projecting optical axis and the mainreflected direction of the axial light reflected by the inclined Fresnelsurface is set between 30° and 45°, an observer can observe a highquality image within a relatively wide field in a comfortable observingposition set outside of the reader.

When the inclined angle of the screen is less than 20°, the screenbecomes too close to the horizontal line, the housing constitutes anobstacle for the observation and the screen is too much falling down toobserve the reader from outside of the reader placed on the desk by anobserver sitting in the natural position, which results in thedistortion of the image. When the inclined angle of the screen is beyond40°, for raising the screen maintaining the necessary light path length,the device becomes big while the observing aperture provided in thehousing becomes small, and moreover, the size of the reflecting mirrorfor bending the optical axis becomes big so that the cost is increased.

The second condition above mentioned is important for effectivelyreflecting and orientating the projected light image, which is projectedon the screen, outside of the housing. Specifically, in the conventionalreflecting type microfilm readers, it was usual to project the lightapproximately perpendicular to the screen, the most of the lightreflected by the screen comes inside of the housing so that thereflected light will be reflected again by the inner walls of thehousing and the mirror arranged inside of the housing so as toilluminate again the screen, and therefore, the construction of thedevice itself causes to deteriorate the contrast.

However, according to the present invention, almost all of the projectedlight exits outside of the housing due to the Fresnel screen, saiddefects peculiar to the conventional devices can be removed.Consequently, a higher contrast and higher quality image is obtainedthan the conventional device under the condition where the externallight will be coming into the housing or where the external light willnot be coming into the housing, which is the ideal condition.

As shown in FIG. 3, the central axis 34 of the Fresnel screen, which isthe common center of the concentric ring strips, is located outside ofthe screen 23, and the end of the screen 23 closest to the central axis34 is placed at a position near to the observing aperture 15 of thehousing. In case of a Fresnel screen in which the Fresnel center islocated within the screen, the observing position becomes inevitablyhigh, so that an observer must take a poor posture which causes fatigue,and moreover, the angle formed by the projecting optical axis and themain reflecting light of the light along the projecting optical axisbecomes small due to the great inclination angle of the Fresnel surfaceso that the selectivity of the reflecting light is small to deterioratethe contrast of the image. The inclined surface of the saw teeth shapedcross section of the usual Fresnel consists of the effective area andthe remaining ineffective area which is the riser portion located at theinterfaces between the adjacent ring strips, and in the optical systemusing a big eccentricity, said riser portion causes the disturbance ofthe image. Especially, in the reflecting type mirofilm reader, theexternal light incident through the observing aperture from theobserving side will impinge on the riser portion of the Fresnel and thisis brightened to disturb the image. This is significant at a portionclose to the observing aperture, which portion is most important forobtaining a good contrast image. Therefore, quality of the image of theportion, which must be seen most clearly, is deteriorated.

According to the present invention, in which the Fresnel center locatesoutside of the screen, it is possible to produce two screens from oneconcentric Fresnel with the aid of a single mold for mass-producing thefine Fresnel surface structure, which is an economical advantage.Further, since the Fresnel grooves formed in the Fresnel surface of thisinvention have no portion connecting to the circles so that any duct orforeign matter on the grooves can be easily swept away along thegrooves.

The screen 23 is, as shown in FIG. 4, made of a mixture of fineparticles 51 of a light reflecting substance and a synthetic resinsubstance 52, and the surface of the screen is formed as Fresnel surfacefor reflecting the incident light to a predetermined direction, and theFresnel surface is provided with fine rugging to diffuse the incidentlight. In FIG. 4, the light 55 incident on the screen 23 is partiallyreflected by the screen surface but the most of the light 55 enters intothe inside of the screen substances where the light isdiffusion-reflected to exit from the Fresnel surface. The lightorientation property of this light exitting from the surface, i.e. thereflected light by the screen, is determined by the probability becauseof the internal diffusion, but this varies by the sort of the syntheticresin and mixing ratio of the synthetic resin and the reflectingsubstance, and the peak of the exitting light is approximately in thepositive reflecting direction. In FIG. 4, the elliptic body 57 shows thedistribution state of the diffusion of the exit light, and the arrowsshown in the elliptic body represent the directions and the intensitiesof the reflected light, respectively, among which the light representedby the arrow 58 is strongest. In FIG. 4, 59 is the normal direction ofthe reflecting surface.

In the above screen, the activity of the diffusion for utilizing it inthe reflecting type screen is obtained by the diffusion-reflectioninside of the screen substrate so that for avoiding the concentration ofthe light reflected by the surface of the substrate to occur in thedirection of the eyes of an observer, the fine ruggings of 1/10 to 1/20of the width of the inclined surface of the Fresnel should be provided.This width of the inclined surface corresponds to the pitch of the ringstrips and is set to be less than 0.2 mm in taking the distance ofdistinct vision and the eye-sight into consideration.

The light orientation property of the screen is controlled by thesynthetic resin constituting the substrate of the screen and the mixingratio of the synthetic resin substance and the reflecting substance. Asthe synthetic resin, an individual or the mixture of at least two kindsof resins, which are non-soluble with each other, is used. In case ofthe latter, by selecting the mixing rate of synthetic resins, it ispossible to reduce the amount of reflecting substance to be mixed, andin this case, a screen having a preferable diffusion characteristic isobtained. Further a transparent or a semi-transparent synthetic resin isused, and when a semi-transparent or translucent synthetic resin of atransmittivity of less than 60% per 0.2 mm is used, the rate of thereflecting substance can be significantly reduced in comparing to thecase where a transparent synthetic resin is used.

The mutual non-solubility relation of various kinds of the syntheticresins is shown in the following table.

    __________________________________________________________________________                      1 2 3 4 5 6 7 8 9 10                                                                              11                                                                              12                                                                              13                                                                              14                                                                              15                                                                              16                            __________________________________________________________________________    polystyrene    1    O O O O O O O O O O O O O X                               polymethacrylic acid methyl                                                                  2  O   O O O O O X O X O O O O O O                             polymethacrylic acid ethyl                                                                   3  O O   X O O O O O X O O   X O O                             polymethacrylic acid n-propyl                                                                4  O O X   X X   O O X O O   X O O                             polymethacrylic acid n-buthyl                                                                5  O O O X   X   O O X O O   X O O                             polymethacrylic acid isobuthyl                                                               6  O O O X X     O O X O O   X O O                             polyacrylic methyl                                                                           7  O O           X O X O O                                     polyacetic acid vinyl                                                                        8  O X O O O O X   O X O O O   O                               acetic acid cellulose                                                                        9  O O O O O O O O   X O O                                     cellulose nitrate                                                                            10 O X X X X X X X X         O                                 ethylcellulose 11 O O O O O O O O O     O                                     benzyl cellulose                                                                             12 O O O O O O O O O   O                                       polyvinyl chloride                                                                           13 O           O O                                             cumarone resin 14 X O X X X X       O                                         polyisobuthylene                                                                             15 O O O O O O   O                                             polycarbonate  16   O O O O O                                                 __________________________________________________________________________     (X: soluble, O: nonsoluble)                                              

In the above table, round (O) marked resins are to be mixed, andespecially, the combination of polycarbonate, polyvinyl chloride andacrylic resins results in a good result. The resins having greatdifference in refractive index should better be combined to obtain agood screen property. In case of combining resins mutually nonsolubleand having different refractive indices, it is possible to obtain anarbitrary internal diffusion-reflection characteristic substrate due tothe difference in refractive index without mixing a reflectingsubstance.

When the rate of light reflecting substance to be mixed in the syntheticresin is increased, the reflecting layer or part of the reflectingsubstance is formed at the position near to the top surface of thescreen, and in an extreme case, each of the reflecting substances willclosely arranged at the near portion of the screen surface, the lightreflected by the screen becomes to the light orientation stateconcentrated at the extremely narrow area around the positive reflectingdirection. Thus by suitably selecting the ratio of mixing it is possibleto obtain a reflecting screen having a suitable light orientationproperty.

When the mixing ratio of light reflecting substance is decreased, thelight enters deeply into the screen substance and by the repetition ofthe internal reflections, the flare of the light is occurred so that incase of decreasing the mixing rate of reflecting substance it is betterto use the aforementioned synthetic resins.

According to the experiments, in view of the resolving power, the depthof the light entering into the substrate should be 0.1 mm-0.2 mm, andthe attenuation of the light per 0.2 mm of the thickness of thesubstrate should be 90-95% to obtain a clear screen having less flare.

It is possible to coloring the screen by mixing dye or pigment in thescreen substances.

FIG. 5 shows a process to produce the screen explained in the foregoing.In FIG. 5(A), a light reflecting substance such as alluminum particlesor powder is uniformly dispersed in the synthetic resin melt of, forexample, acrylic resin, and the resulted melt 60 is put onto the mold61, which has the shape of a surface opposite to the Fresnel surface ofa Fresnel concave lens, and each of the inclined surfaces is of a finerugging surface 62. The sheet obtained after cooling the heated melt 60is separated from the mold to provide the screen. The light image isprojected on the back surface, which is faced to the mold 61, of thesheet and the screen is observed from the same side as the image wasprojected.

In FIG. 5(B), similar mixing melt 60' was coated as a thin layer on thesimilar mold 61' and a supporting body 65 is overlaid on the mold 60'and after cooling, the thin sheet 60' and the supporting body 65 areintegrally separated from the mold 61' to obtain the screen. Forimproving the separation, the surface of the mold 61' should better becoated by an agent such as Teflon, i.e., ethylene fluoride resin foraiding the peeling off of the sheet. It is possible to form firstly thethin sheet 60' and then supporting body 65 is put on the sheet 60' byusing an adhesive. According to the method of FIG. 5(B), the thin layerof the mixed melt 60' is obtained so that only a short time is requiredfor cooling, and moreover, a continuous flexible sheet can be obtainedso that it is suitable for a mass-production at a less expense. Further,even when an uneven thickness of the sheet is obtained, the back surfaceof the separated sheet is formed as a faithful Fresnel surface so thatthere is no problem. In any case, each of the ring strip reflectingsurfaces of the screen is formed to have a predetermined correctinclined angle, the screen having a definite quality and property can beeasily produced.

As a light reflecting substance, nickel, chromium, aluminum oxide (Al₂O₃), barium sulfate, zinc oxide, magnesium oxide, etc. is used in theform of a fine cube, spherical or thin piece.

FIG. 6 shows the state of distribution of the light diffused andreflected by the screen of the light incident into the screen, in which140 represents the position of the pupil of the lens, 142 the eyes of anobserver, 145 peripheral light source outside of the housing of thereader. The incident light 141 from the pupil 140 is diffused andreflected by each of the ring strips 23' of the screen 23, and thereflected light is distributed as represented by the elliptic body 141'shown by real lines and the reflected main light 141" having the highestintensity among the exit lights from the ring strips 23' enters into theeyes 142 of the observer positioned at the standard location. Thus theintensity of the light directed to the observer is substantiallyincreased and the whole surface of the screen becomes uniformly andgreatly lightened. On the other hand, the incident light 146 from theexternal light source 145 is diffused and reflected by each of the ringstrips 23' and the reflected light is distributed as shown by theelliptic body 146' of the dotted line. Thus the reflected main lightcomponent 146" having the highest intensity among the exit light fromeach of the ring strips 23' is not directed to the eyes of the observerso that the ratio between the image light and the external light amongthe reflected light components directed to the observing side becomessmall in comparing to the actual rate of the intensity of the lightincident on the screen and a good contrast projected image can beobtained.

The screens shown in FIGS. 7 and 8 represent other embodiments,respectively. The screen 223 shown in FIG. 7 provides with rugging layer231 on the surface of the substrate 230 having a surface correspondingto the Fresnel surface of Fresnel type concave lens. On the surface ofthe rugging layer 231, a thin light reflecting surface 232 is provided.This screen comprises a substrate formed with thick paper, metal andsynthetic resin etc., on which the Fresnel surface is formed and thepaint having fine particles of TiO₂, SiO₂ and ZnO etc., is uniformlycoated along the Fresnel surface and dried to form on the surface thefine rugging. On this coated surface, the reflective metal of, forexample, aluminum is deposited to form a thin layer to obtain thescreen. The surface of the light reflecting layer 232 has the finerugging by the fine particles of the inner layer to have a diffusionproperty necessary for the screen.

The screen 323 shown in FIG. 8 provides with the light diffusion layer331 on the surface of the substrate 330 comprising Fresnel type concavemirror. This screen is formed by coating a paint having fine particlesof light diffusive material on the surface of Fresnel type concavemirror and drying it. It is also possible to obtain the screen bycoating a paint of the light reflecting substance mixed with the fineparticles of the light diffusive material on the substrate havingFresnel surface. The diffusivity of this screen can be varied bychanging the shape of the particles of the light diffusive substance.

The light orientation characteristics of the light reflected by thescreen of the invention are shown in FIG. 9. The measurements were madeby assuming 0° the direction of the light reflected to the normaldirection of the ring strip surface by applying a definite light at anangle of 45° on one of the ring strips of each screen and by measuringthe intensity of the reflected lights received on the plane includingsaid 0° direction light and varying the angle of reflection. Each angleof the reflection is shown in the abscissa and the ratio of quantity ofreflected light to incident light quantity relative to the incidentlight quantity, which is assumed as 10⁵, is shown in the ordinate ofFIG. 9. The results were shown in FIG. 9, in which the curve Aassociates with the screen 223 shown in FIG. 7, curves C₁, C₂ and C₃ andD associates with the screen 23 of FIG. 4. The curves C₁, C₂ and C₃ wereobtained by using acrylic resin as a synthetic resin and varying themixing rate of the aluminum powder and setting the light transmittivityper 0.2 mm of the mixture as about 5%. The aluminum powder is a fineparticle of scale shape and the maximum size thereof is about 20μ. Thecurve C₁ is obtained by using the aluminum of mixing rate of 0.5weight%, the curve C₂ is obtained by using 1 weight% of aluminum and thecurve C₃ is obtained by using 2 weight% of aluminum. The curve D isobtained by using the mixture rate 2:1 of polycarbonate resin relativeto acrylic resin, the mixture being the mutually non-soluble resins towhich aluminum powder is added at a rate of 0.05% relative to the resinmixture. In FIG. 9, the screen is dark when the peak of the curve is lowand the screen is light when the peak of the curve is high. It ispreferable to select the screen of good light orientation property whichcorresponds to the curve having a high peak for preventing the effectsof the peripheral light to deteriorate the contrast of the projectedlight and for observing a high brightness image. However, if the lightorientation property is extremely good the field to see the projectedimage becomes narrow so that it is necessary to suitably control thelight orientation property.

According to the screen of FIG. 4, an optional light orientationproperty can be easily obtained so that a high quality screen is easilyproduced.

The present invention can be applied not only to film reader but also toreader printer.

What we claim is:
 1. A film reader comprising:a housing having anobservation aperture; means for illuminating a film having an imagerecorded thereon; means for projecting an image of film illuminated bysaid illuminating means; a reflection type screen obliquely disposed insaid housing in opposition to said observation aperture for allowing anobserver to observe an image of film projected by said projecting means,said screen having a number of concentrically arranged reflectingannular surfaces having inclination angles which increase in a directionaway from a common center of the annular surfaces, and said screenhaving a saw-like cross-section, said adjacent reflecting surfaces beingjoined by risers; wherein said common center is located outside saidscreen, and adjacent an edge of said screen which is in the neighborhoodof said observation aperature; whereby said risers are not visible tothe observer.
 2. A film reader according to claim 1, in which the planeof the screen surface is inclined by an angle of between about 20° andabout 40° relative to the horizontal plane, and the ring strip surfacesreflect a main beam which is incident along a projection optical axis sothat an angle formed between the main reflected beam and the incidentbeam is between about 30° and about 45°.
 3. A film reader according toclaim 2, in which said illumination means is located at a lower portionof said housing while said optical means, having a projection lens, islocated at an upper portion of said housing, said optical means furtherincluding a mirror for directing the light which has passed through saidprojection lens to said screen.
 4. A film reader comprising:a housinghaving a viewing aperture; and optical means for illuminating a filmbearing reduced images and for projecting an image of the illuminatedfilm onto a screen which is arranged within said housing so as to beviewed through said aperture; said screen having a series of concentricannular surface portions constituting a Fresnel condensing surface theoptical axis of which is at the common geometric center outside saidscreen, and said screen being arranged to reflect light projectedthereon through said aperture with that portion of the screen peripherywhich is closest to said center lying nearest to said aperture, wherebythe risers between adjacent annular surfaces are not visible to anobserver at an observing position.